Electrolytic system



May 2, 1961 RC. SABINS ELECTROLYTIC SYSTEM Filed June 2, 1958 INVENTOR. HOLLAND C.SABINS W BYH United States Patent Ofice 2,982,714 Patented May 2, 1961 r g ELECTROLYTIC SYSTEM. v Rolland c. Sahins, 522 Catalina Blvd.,

'San Diego6, Calif. Filed June 2, 1958, Se. No. 739,104 Claims. Cl. 204196) the submerged structure such'as the hull of a ship or a barge. Such means has been found to be unsatisfactory because of the varying current requirements necessary to provide adequate protection for the submerged structure. I As is Well known, the current requirement to provide satisfactory protection is dependent upon many factors as for example, the speed of movement of the hull through the water, temperature, and ionic content of the water through which the hull is moving, etc. Attempts to provide automatic control to take care of these variations have heretofore not been completely satisfactory. This, in large part, has been due to the fact that apparatus of this type must function for long periods of time without maintenance because a ship carrying the system may not return to its home port for months and even years. Automatic control is also complicated by the fact that the sys-' tern must operate over a wide range of impressed currents. It must respond to very small control currents and must provide magnification of a very high order. There is a need for an automatic control system which will be suitable for use on large vessels and which will require very little, if any, maintenance.

In general, it is an object of the present invention to provide a control system and method which will automatically control the current impressed on the structure to be protected to maintain the structure at a predetermined polarization. v

Another object of the invention is to provide a system and apparatus of the above character in which the current Further objects and advantages will be apparent from the following description, reference being had to the acimpressed on the structure is determined by the reference current.

Another object of the invention is to provide a system of the above character in which a reference cell is utilized in a monitoring circuit for generating a reference current.

Another object of the invention is to provide a system of the above character in which the reference cell is maintained at its standard reference level.

Another object of the invention is to provide a system of the above character in which a reference cell is always connected to the monitoring circuit.

Another object of the invention is to provide a system of the above character which has practically no moving parts.

Another object of the invention is to provide a system of the above character which requires very little, if any, maintenance.

Another object of the invention is to provide a system of the above character in which the response is almost instantaneous and closely follows the demand.

companying drawings wherein a preferred embodiment of the invention is illustrated.

The drawing is a circuit diagram incorporating they present invention with certain parts illustrated schematically. A

In general, the present inventionvcomprises. a control system and method for automatically. providing cathodic protection .for various types of structures such as the hulls of vessels and barges andlike normally immersed or submerged in fresh or salt water or other electrolyte. A current is impressed on the-structure to cause the structure to serve as a cathode. A monitoring circuit is provided in which a reference current is generated and this reference current is utilized indirectly for controlling the amount of current impressed on the structure to maintain the structure at a relatively constant predetermined polarization to prevent corrosion of the structure.

As shown in the drawing, my control system comprises generally an impressedcurrent power supply 11, monitoring means whichincludes a reference current supply and control 12 and means 13 for maintaining a reference cell at its standard reference level. rent supply 11 is connected between an anode assembly 14 and a structure 16 to be protected which is represented as ground. The anode assembly 14 and the structure 16 are shown submerged or immersed in anelectrolyte 17 which, ;for example, can be seawater. The structure to be protected can be the hull of a ship as shown and the anode assembly 14 can be of any suitable type such as that disclosed in my copending application entitled Electrolytic System, Serial No. 715,440, filed February 14,

The monitoring means 12 includes a reference cell 21 which is utilized for generating a reference current. As shown, the reference cell is also submerged in the electrolyte .17 and is generally mounted relatively close to the structure 16 to be protected 'The reference cell can be of any suitable type such as the silver-silver chloride reference half cell well known to those skilled in the art. Such reference half cell has a potential in the electrolyte 17 which differs from the potential of the structure 16 when it' is submerged in the electrolyte so that there is a current flow between the reference cells and the structure 16 to be protected. When a reference cell of the silver-silver chloride type is utilized, the reference cell has a relatively uniform potential which is approximately 630 'millivolts lower than that of a steel hull of a ship, if

for example, that is the structure to be cathodically protected.

" When the reference cellis connected by a conductor to the hull of the ship, current will fiow through the electrolyte 17, from the hull of the ship to the reference half cell. By'current flow, I am referring to the flow of electrons from negative to positive or rather a lower negative than the conventional designation of current flow from positive to negative.

' As is well known to those skilled in the art, the silversilver chloride reference half cell has a relatively constant potential when immersed in an electrolyte and for that reason the current'fiow from the hull of the ship to the reference half cell will be dependent upon the polarizationlevel' on the hull of the ship or the structure being cathodically protected. When the polarization level of the ship rising, the current flow between the hull of the ship and the reference half cells will increase, and

The impressed curhalf cell is normally connected by a conductor 24 to the positive terminal of a meter 26, the negative terminal of the meter being connected to ground as. shown. As pointed out previously, all points designated as ground, are actually connected to the structure 16 to. be protected as, for example, the ships ground whenthe hull designated as positive. This has been done because even though the reference cells .are actually negative, they are less negative than'a steel hull and thus are positive with respect to the steel hull or structure 16. The reference cell has been designated in'this manner to facilitate understanding of the direction of current flow, i.e., electron flowing from the hull to the cell 21'.

The meter 26, as shown schematically, includes a needle-like pointer or hand 27 which has a spade-like tip 28. The dial 29 of the meter is provided with-a hole 31 which is' adapted to be covered by the spade-like tip 28 of the pointer when the meteris indicating a midpoint position as shown in the drawing. A stop 32 is provided on the dialface to prevent the pointer from advancing beyond the midpoint of the dial. Since the meter 26 is connected in series between the reference half cell 21 and the structure to be protected, it is apparent that the meter 26 will register the electron current flow between the structure 16 and the reference half cell 21 to which it is connected.

A suitable light source such as a lamp 34 is positioned on one side of the dial face 29, for example, as shown it is positioned in front of the dial face. The lamp 34 is connected to a suitable source of power such as 110 volts, 60 cycle single phase A.C. as designated by the terminals L1 and L2. As shown, the lamp is connected across the terminals L1 and L2 through a variable series resistor 36. The lamp 34 is preferably of a type with a very long life such as years. 1 The resistor 36 is provided to vary the intensity of the light from the lamp.

Suitable light sensitive means 37 is mounted on the other side of the dial-face opposite the opening or hole 31. For example, a polycrystalline photoconductive cell can be utilized. Particularly, a cadmium-selenide photocell has been found to be especially satisfactory. The

out the induced current and thereby preventing the buildup of dangerous voltages within the other windings of the reactor.

The bias winding 46 is wound in the opposite direction to that of the mainsaturating winding 43 and its purpose is to bias the output of the A.C. windings 44 to cut ofi when saturating current is not applied to the saturating windings. The bias winding 46 is supplied from the A.C. power supplydesignated by the lines L1. and L2 through a transformer 49 which has its output connected to a pair of suitable rectifiers 51. The rectifiers 51 are connected to one side of the bias winding 46and the other side of the bias winding is connected to the center tap 52 of the secondary winding of the trans-former 49 through a serially connected shunt resistance 53 and a variable resistance 54. An ammeter 56 of a suitable type, such as a D.C. milliammeter, 'is connected across'theshunt resistance 53. The variable resistance54 is provided to light sensitive means 3'7 is preferably mounted relatively close to the hole 31 and, for example, may be mounted within the meter housing itself if desired.

As shown, the output of the light sensitive means 37 is connected to a power reactor 39 in series with an ammeter 41. The ammeter 41 is of any suitable type such as a very sensitive D.C. microammeter. The power reactor 39 is of'the saturable core type with duplex windings wound on a pair of toroidal cores. As shown, the reactor 39 comprises a pair of toroidal cores 42, a D.C. saturating winding 43, a pair of A.C. or output windings 44, a D.C. bias winding '46, and a D.C. shorted winding'47.

The shorted winding 47 is provided to prevent breakdown of the insulation within the power reactor 39 and to prevent damage to other components in the circuit hereinafter described. In the event the A.C. power to the A.C. output windings 44 should be suddenly interrupted, the suddencollapse of the lines of force inthese coils would normally induce several thousand volts into the D.C. windings of the reactor and, therefore, would have a tendency to causethe damage hereinbefore described, However, the shorted coil which has a 'very low impedance prevents such an occurrence by shorting adjust the flow of current in the bias winding 46. As is well known to those skilled in the art, the current flow in the bias winding must be carefully adjusted so that the load from the output, windings 46- is zero when the input to the D.C. saturating winding is at zero.

As shown, one side. of the output of the light sensitive means 37 is connected to one side of the D.C. saturating winding 43 and the other side of the D.C. saturating winding is connected to the center tap 52 of the secondary of thetransformer 49. The other side of the output of the light sensitive means is connected to the side of the bias winding 46 which is connected to the rectifiersSl.

The output of the A.C. windings 44 of the reactor 39 is connected across a full wave bridge 59 comprising four rectifiers 61. The center tap 62 between the A.C. windings 44 is connected to the A.C.linefiLZ by a conductor 63. The other side of the rectifier, bridge is connected to the A.C. line L1 by conductor65.

The output from the full wave bridge 59 is supplied to the power reactor 64. The power reactor 64 comprises a pair of closed C-type cores 66, a pair of D.C. saturating windings 67, four A.C. windings 68, a variable resistance 69 and a fixedresistance 71. The power reactor 64 is wound in such a manner that magnetic opposition is provided under all operating-conditions and for that reason a bias winding of the type provided in the power reactor 39 is not required. A bias is also not used because the winding arrangement utilized in the power reactor 64 is not of a type which lends itself to the use of a bias winding. The windings and the corematerial have been chosen sothat the output of the A.C. windings 68 is zero or substantially zero When there is no input to. the D.C. saturating windings 67. V

The output of the full wave bridge 59 is connected across the serially connected D.C. saturating windings 67. of thepower reactor 64 by conductors 73 and 74.

An ammeter 7-6 is connected in a series with the conduc-,

tor 74 and can be of suitable type such as a D.C. millia'mmeter. V

It will be noted that the resistances 69 .and 71 are serially connected across the conductors 73 and 74 and in parallel with the D.C. saturating windings 67. These resistances .69 and 71 have been" inserted in the power reactor because it was found that the normal sinusoidal full wave D.C. output from the full wave bridge 59 would not cause proper operation of the.D.C. saturating windings 67. In fact, it was found that the saturating windings 67 were actually acting as" a choke coil because of the back induced by the rapidly fluctuating sinusoidal full wave D.C. By utilizing the re-. sistances 691 and 71 in parallel with the D.C. windings, the resistances serve to bypass or cut off the peaks of the sinusoidal output from the full wave bridge. Thus, the D.C. peaks pass through the resistances and not through the D.C. saturating windings. .The rapid fluctuations of the D.C. in the windings 67 and the generation of back are eliminated. It is apparent that dapacitors could be utilized for the same purpose of snioothingout'the *D.C. However, resistors have been chosen because they have much longer life. A pi type filter can also be used for such'a purpose and can consist of iron core inductance and a pair of dry plate type capacitors.

The output of the power reactor 64 is fed into an A.C.- D.C. rectifier section 78. As shown, the four A.C. windings of the power reactor are connected in series opposition and have one end connected to the A.C. or conductor 65 and the other end connected to the primary winding of an isolation transformer 79. The other side of the primary is connected to the line L2 of the A.C. supply. The secondary of the isolation transformer is connected across a full wave bridge 81 comprising four rectifiers 82. The positive terminal of the output of the full wave bridge 81 is connected to the anode assembly 14 by a conductor 83, and the negative or ground terminal of the bridge is connected to the structure '16 by conductor 84. A DC. arnmeter 86 is connected in series with the conductor 83. A DC. voltmeter 87 is connected across'the output of the full wave bridge 81. Operation of that proportion of the system hereinbefore described may now be briefly described as follows: Let it be assumed that the millivoltmeter 26 has been adjusted by adjustment of its external resistance (not shown) so that, at the desired polarization on the structure 16, the needlelike pointer 2'7 of the meter is at its midpoint position and the spade-like tip of the needle is covering the hole 31 in the dial face. The spadelike tip 28 in this position prevents the entrance of lightrays: through the hole 31 and therefore prevents-activation' of thelight sensitive means 37.' The pointer 27 in-this position is against the needle stop 32 so that at increased polarization levels of the structure 16 above the desired polarization, no light can pass through the opening 31. r

. Now. let it be assumed that the structure 16 has dropped below the desired level .of polarization which is required for. cathodic protection. When this occurs, the potential difference between the reference cell 21 and the structurelddecreases, which in turn causes a decrease in. thereferende current flow in direct proportion to the decrease in the potential difference. The difference in the decrease in the current flow is registered by the meter 26 and the pointer 27 begins to move towards a decreased current position. As soon as the pointer 27 has moved from-its midpoint position, the spade-like tip 28 exposes the hole 31 and permits light from the lamp 34 to enter the hole and activatethe light sensitive means or cell 37. a i

Activation of the light sensitive cell 37 reduces its resistance sothat it permits substantial current flow in the DC. saturating windings 43 of the power reactor 39. Current flow is from the center tap 52 through the DC. saturating winding 43, through the resistance of the light sensitive cell 37, through the microammeter 41 and to the positive side of the rectifiers 51.

The flow of current through the DC. winding 43- saturates the toroidal cores 42 to permit flow of A.C. current in the output windings 44, by eliminating the impedance in'the output windings 44. The AC. output from the windings 44 is rectified by the full wave bridge 59 and the DC from the bridge is supplied to the DC. saturating windings 67 of the power reactor 64. The flow of DC current in the saturating windings 67 saturates the cores 66 which reduces the impedance in the A.C. windings 68 to permit A.C. to pass through these power windings and to energize the isolation transformer 79. The A.C. output from the isolation transformer is rectified by the main full wave bridge 81 to deliver a positive DIC.-current to the anode array 14. The negative terminal of the bridge 81 is connected to the structure 16 to be protected. I

' The increased potential impressed on structure 16 from the anode assembly 14 and through the impressed current also increase causing the millivoltmeter 26 to register an increase. This will continue until the spade-like tip 28 of the pointer 27 again covers the hole 31 in the dial 29.

From the foregoing description, it is apparent that as soon as the polarization level of the structure 16 drops below the predetermined desired level, the spade-like tip 28 will uncover the opening 31 to cause a sequence of operation which will increase the current fiow between the structure 16 and the anode 14 until the increase is sufficient to raise the polarization level of the structure 16 to the desired level. Thus, the polarization level of the structure 16 is maintained relativelyv constant. If there are no changes in the polarization level, the spadelike tip 28 will cover the opening 31 and a relatively constant flow of current will occur between the structure 16 and the anode 14. When there are changes in the polarization level, the response of the system is almost instantaneous and the polarization is rapidly built up to the desired level.

As hereinbefore described, my system includes means 12 for continuously monitoring the polarization on the structure being cathodically protected. This monitoring meanswhich has also been referred to as the reference and current supply hasibeen previously described as including reference cell 21. It has been found that reference half cells do not maintain an absolutely constant level of polarization, but that when they 'are subjected to various environments and are employedin a'c'athod'e anode couple, they gradually become negatively polarized. When this occurs, a reference cell fails to serve the function of a'constant reference.

When, for example, a silver-silver chloride reference cell is used as a reference to a steel hull, a sacrificial cathode-anode couple exists between. the two when im-' mersed in a seawater electrolyte, the steel ship being. the anode in this couple and the silver-silver chloride cell being the cathode; therefore, inasmuch as' the electron' flow is from the steel hull through the meter resistance and conductor to the silver metal of the cell thus the energy transfer from the steel to the silver tends to cause I have found that the cathodic state of the reference cell can be maintained relatively constant if a second circuit is employed between the ship and reference cell utilizing an impressed current means to reversethe direction of electron flow of the first mentioned sacrificial couple wherein the impressed current means causes the silver of the cell to become the anode with respect to the ship establishing an anode cathode couple withthe electron flow from the silver cell through the impressed means to the steel hull, polarization level of a reference cell such as the reference half cell 21 can be maintained, for all practical purposes, at a constant level. To accomplish this, I provide a stabilizing circuit in the form of a DO. circuit including a source of current, the cell 21,

connected to A.C. line L1 and the other side to the A.C. line L2. The ends of the secondary winding being connected to a rectifier assembly 92 including rectifiers 106. A variable resistance 107 is connected between a tap on the secondary of the transformer 91 and ground.

The system functions as follows:

Let it be assumed that. to cathodically protect the struc ture 16 that it is necessary to maintain the structure 16 at a predetermined polarization level with respect to the reference cells. 21, as for example, 1000 millivolts. If such is the case, the resistance 107 of the rectifier assembly 92 is adjusted so that the rectifier assembly 92 will deliver a somewhat high voltage, for example 1020- millivolts on the structure 16 (hull) through the ground connections.

The reference cell 21 is always connected to the millivoltmeter 26 by the wire 24. As explained previously, when the reference cell 21 is connected to the structure being protected through the rnillivoltmeter 26, there is an electron flow from the structure being protected to the reference cell.

Thus two circuits are present at all times. One of these circuits comprises the hull 16', the grounds at the hull and the meter 28, the high resistance meter 26, conductor 24, cell 21, and the electrolyte (sea water). The electron flow in that circuit is from the cathodic hull toward the cell 21. The other of these circuits compr' es the secondary of transformer 91, the rectifier 92, conductor 24, cell 21, electrolyte (sea water), hull 16, the grounds at the hull and at the variable resistance, and the variable resistance; the electron flow in this last circuit, with respect to the cell 21 is opposite that of the next preceding circuit. The'ultimate result is, that the polarization level. of cell 21 is maintained,.for all practical purposes, constant regardless of length of time.

If this current flow in the stabilizing circuit is adjusted to approximately, or slightly more or slightly less than the same amount of current that is flowing in the.sacri ficial couple of opposite direction, the amount of energy influence on the silver is almost nil; therefore, it remains. in its normal anodic state and consequently remains a re.- liable reference base. The current flows of these two circuits, connected to the same two components, do not-influence each other to any perceptible degree since the sacrificial circuit or reference, circuit employs a high resistance voltmeter in series relationship and this high resistance blocks the impressed currents from shorting back to ship, since the silver, seawater, hull path is relatively a very low resistance path. This low resistance circuit of the impressed current means lowers the potential of this circuit, at the desired current flow, to such a low value that it is not perceptible on the reference meter, especially at adjusted optimum levels.

The cell 21 is preferably of the type shown and described in the aforementioned co-pending application.

By way of example, one embodiment of my system utilized components having thefollowing designation, Values and characteristics:

Diodes;

511N1084 61-1N1092 82--1N1167 and 1N1l81 106-1N1084 Photocell:

, 37Clairex Type CL-3 Transformers:

49-110 volts to 25 volts 91--1l0 volts to-25 volts 79-1:1 ratio, 1000 watt capacity Saturable core reactors:

39-output of 500 milliamperes 64-1000 wattcapacity Meters:

26-2 ,500-maximum millivolts adjustable 4-0-500 microamperes 8 56---0.-1 milliampere-shunted to obtain microampere range 76'---0500 milliamperes 87-0-100 volts 86-0-100 amperes Resistances:

36wire wound 125 ohms 54-wire wound 1000 ohms 69--wire wound 500 ohms 71wire wound 25 ohms 107-wire Wound l megohm desired It has been found that a system having the above components, hasxample capacity to provide complete cathodicv protection for a ship 15.0 feet in length: with a steel hull,

and having approximately 5000-6000 square feet of wetted surface. With the 1000 watts available from such a system, the ampere voltage ratio. is automaticallydetermined by the ratio. of the surface of the anode assembly 14 utilized and the wetted surface of the struc-' ture to be protected, and the resistivity of the water or. electrolyte. Thus, if a 1:1 isolation transformer 79' is. utilized and the isolation transformer is driven from a 115 volt, 60 cycle, single phase D.C. supply and the power reactor 64 is being driven at its full 1000 watts output, the DC. voltage on the output read by the meter 87 would be approximately 20 volts and the amperes; read by the meter 86 would be approximately 50. am-;

peres, assuming that the proper amount of anode surface. was utilized to obtain the proper anode-cathoderatio, and also assuming that the structure is in water having a relatively high resistance. If the structure.- were a vessel operating in the equatorial zones in warm water with: low resistivity, the DC. voltage might be'as low.as 1.0 volts vw'th amperes D.C. V

With a system of the above type having an: output of 1000 watts, an amplification of two hundred million to one is achieved by only two stages of amplification as represented by the reactors 39 and 64. The reference cell 21 has an output of approximately 10 microwatts. Only one-half of the output, 5 microwatts, is utilized for driving the meter 26. These 5 microwatts are amplified into the 1000 watts in the output to give the two hundred million to one power amplification. 1

Since the current flow from the structure. being protected such as the hull of a ship to theanodes 14 determines the polarization level of the. structure being protected, it is important that a wide range of current flow be obtainable from any satisfactory system. Generally, it is desirable to obtain a 50 to 1 variation in current flow. With my system, it has been found possible to.- obtain a' 100- to 1 variation in the current flow.

I have found by utilizing the light sensitive cell- 37, precise control can be obtained on the polarization level of the structure being protected. If the polarization level of the structure being protected should drop only a very slight amount below the desired level, the system immediately determines this condition and responds practically instantaneously to increase the current flow from the impressed current means. The system is instantly cognizant of any changing conditions which may require increased or decreased current flow, as for example, in the case of a vessel which is passing through water which has different resistance characteristics than that previously passed through.

It is apparent from the foregoing that I have provided a completely automatic control system and method for maintaining a desired polarization level on a structure to be cathodically protected. There are no moving'parts in the system except for the meter movements which have an extremely long life. Thus, in contrast to other systems, my system has no mechanical relays, contact points, servo mechanisms, variacs or'other' moving parts which would require extensive and continued maintenance. By utilizing saturable'core. reactors, magnifications of a high order are obtained by devices which have utilization of the light sensitive means, a particularly precise control is obtained which has an almost instantaneous response and which closely follows the demand on the system. Such performance coupled with the lack of maintenance is particularly important in systems of this type which are often installed in large ships which may not return to their home ports for long periods of time. If this were not the case, a breakdown of the system while the ship was out of port could permit severe damage to occur to the hull of the ship before the system could again be placed in operation.

It is also apparent that in addition to being useful for the cathodic protection of the hulls of ships, barges and other floating vessels, my system can be used for cathodically protecting other structures such as underwater foundations, pipelines, storage reservoirs, and the like.

While the form of embodiment herein shown and described constitutes a preferred form, it is to be understood that other forms may be adopted falling within the scope of the claims that follow.

I claim:

1. In a control system for cathodically protecting a structure immersed in an electrolyte, an anode immersed in the electrolyte; means connected to said anode and said structure to impress a .current flow between the anode and the structure to cause the structure to serve as a cathode; a single reference .electrode immersed in p the electrolyte, the reference electrode having a relatively constant potential in the electrolyte which differs from the potential of said structure to be cathodically protected; a constantly closed reference circuit in which a reference current flows between the structure and the reference electrode, said reference circuit including said structure, said electrolyte, said reference electrode and a current responsive device all connected in series circuit relationship; means responsive to the reference current flow in said current responsive device between the reference electrode and said structure to regulate said first means to maintain a relatively constant predetermined polarization potential on said structure; and means providing a constantly closed circuit including a source of current, said structure, said single reference electrode, and the electrolyte, for maintaining the potential of the reference electrode at a substantially constant level.

2. A control system as in claim 1, wherein said reference electrode has a potential which is lower than the potential of said structure.

3. A control system as in claim 1 wherein said reference electrode is a silver-silver chloride half cell.

4. In a method for cathodically protecting a structure immersed inan electrolyte, which method comprises, impressing a current flow between an anode and said structure to cause the structure to serve as a cathode, providing a reference current flow through a single reference electrode, the electrolyte and said structure, the reference current flow being determined by the difference between the polarization levels on said structure and said reference electrode, regulating the flow of impressed current in accordance with the reference current flow, and impressing a source of current on the reference electrode having an electron flow inopposition to the electron flow of the reference current.

5 In a method for cathodically protecting a structure immersed in an electrolyte, which method comprises, impressing a current flow between an anode and said structure to cause the structure to serve as a cathode; providing a reference flow by establishing a constantly closed circuit including the structure, the electrolyte, and a single reference electrode, the reference current flow in said circuit being determined by the polarization levels on said structure and the single reference electrode; regulating the flow of impressed current in accordance with variations in the reference flow; and providing a source of current whose circuit is constantly closed and constantly includes said structure, electrolyte, and reference electrode and having an electron flow in opposition to the electron flow in the reference circuit.

6. In a method for cathodically protecting a structure immersed in an electrolyte, which method comprises, impressing a current flow between an anode and said structure to cause the structure to serve as a cathode; providing a reference flow by establishing a'constantly closed circuit including the structure, the electrolyte, a reference electrode, and a current responsive element responsive to current flow in said circuit, the reference current flow in said circuit being determined by the polarization levels on said structure and the single reference electrode; regulating the flow of impressed current in accordance with variations of current flow in said current responsive element; and providing a source of current whose circuit is constantly closed and constantly includes said structure, electrolyte, and reference cell and having an electron flow in opposition to the electron flow in the reference circuit, the E.-M.F. in the last mentioned circuit being of different (higher also lower) value than that of the reference circuit.

7. The method as defined in claim 6, characterized in that the in the last mentioned circuit is of higher value than that of the reference circuit.

8. In a control system for cathodically protecting a structure immersed in an electrolyte, an anode immersed in the electrolyte; means connected to said anode and said structure to impress a current flow between the anode and the structure to cause the structure to serve as a cathode; a single reference electrode immersed in the electrolyte, the reference electrode having a relatively constant potential in the electrolyte which differs from the potential of said structure to be cathodically protected; a constantly closed reference circuit in which a reference current flow between the structure and the reference electrode, said reference circuit including said structure, said electrolyte, said reference electrode and a current responsive device all connected in series circuit relationship; means responsive to the reference current flow between the reference electrode and said structure to regulate said first means to maintain a relatively constant predetermined polarization potential on said structure; and means providing a constantly closed circuit including a source of current, said structure, said reference electrode, and the electrolyte, said source of current being D.C. and the electron flow thereof through the structure, reference electrode and electrolyte being counter to that of the reference current.

9. A control system as defined in claim 8, characterized in that the reference electrode functions as a cathode in one of the aforementioned circuits in which it is in cluded and functions as an anode in another of the aforementioned circuits in which it is included.

10. A control system as defined in claim 8, characterized in that the reference electrode functions as a cathode in the reference circuit and functions as an anode in the last mentioned circuit.

References Cited in the file of this patent UNITED STATES PATENTS 2,221,997 Polin Nov. 19, 1940 2,759,887 Miles Aug. 21, 1956 2,765,986 Pompetti et al. Oct. 9, 1956 2,918,420 Sabins Dec. 22, 1959 FOREIGN PATENTS 669,675 Great Britain Apr. 9, 1952 OTHER REFERENCES Anal. Chem, vol. 23, pp. 941-944, DeFord. 

1. IN A CONTROL SYSTEM FOR CATHODICALLY PROTECTING A STRUCTURE IMMERSED IN AN ELECTROLYTE, AN ANODE IMMERSED IN THE ELECTROLYTE; MEANS CONNECTED TO SAID ANODE AND SAID STRUCTURE TO IMPRESS A CURRENT FLOW BETWEEN THE ANODE AND THE STRUCTURE TO CAUSE THE STRUCTURE TO SERVE AS A CATHODE; A SINGLE REFERENCE ELECTRODE IMMERSED IN THE ELECTROLYTE, THE REFERENCE ELECTRODE HAVING A RELATIVELY CONSTANT POTENTIAL IN THE ELECTROLYTE WHICH DIFFERS FROM THE POTENTIAL OF SAID STRUCTURE TO BE CATHODICALLY PROTECTED; A CONSTANTLY CLOSED REFERENCE CIRCUIT IN WHICH A REFERENCE CURRENT FLOWS BETWEEN THE STRUCTURE AND THE REFERENCE ELECTRODE, SAID REFERENCE CIRCUIT INCLUDING SAID A CURRENT RESPONSIVE DEVICE ALL CONNECTED IN SERIES CIRCUIT RELATIONSHIP; MEANS RESPONSIVE TO THE REFERENCE CURRENT FLOW IN SAID CURRENT RESPONSIVE DEVICE BETWEEN THE REFERENCE ELECTRODE AND SAID STRUCTURE TO REGULATE SAID FIRST MEANS TO MAINTAIN A RELATIVELY CONSTANT PREDETERMINED POLARIZATION POTENTIAL ON SAID STRUCTURE; AND MEANS PROVIDING A CONSTANTLY CLOSED CIRCUIT INCLUDING A SOURCE OF CURRENT, SAID STRUCTURE, SAID SINGLE REFERENCE ELECTRODE, AND THE ELECTROLYTE, FOR MAINTAINING THE POTENTIAL OF THE REFERENCE ELECTRODE AT A SUBSTANTIALLY CONSTANT LEVEL. 